The present invention relates to fire retardant or fire resistant styrene polymer foams and in particular, relates to fire resistant or fire retardant styrene polymer foams having reduced brominated fire retardant.
Over the past several decades, polymer foams have become available in a wide variety of forms, either in answer to a material need in industry, or as a developmental expansion of commercialized precursors. Some of the more popular forms of foamed polymer. compositions take the shape of films, sheets, slabs and profiles. Generally, these products are produced by extrusion methods in which the polymer is converted by heat and pressure into a homogeneous melt and forced through a die into the desired shape. To obtain a cellular structure, the plastic usually incorporates a blowing agent that decomposes under the heat of the extrusion process and releases gases that cause the shape to expand. It is also possible to inject propellants directly into the melt.
Because of the favorable combination of properties, price and ease of processing, styrene polymers, especially polystyrene, are widely used in preparing foam sheets, films and slabs for such divergent end uses as packaging, pipe and tubing, construction and insulation. For example, expanded styrene polymers such as polystyrene are widely used in the insulation of freezers, coolers, truck bodies, railroad cars, farm buildings, roof decks and residential housing. Styrene polymer foams are also used as the core material for structural sandwich panels used in refrigerated truck bodies, mobile homes and recreational vehicles.
There is an increasing demand for improving the fire retardant properties of materials used in vehicles, the building trades and consumer goods, such as furniture, radio and television cabinets, appliance housing, electrical motor housings, and switch boxes. To meet this demand, various steps have been taken to improve the fire retardant properties of thermoplastic polymers in order to make them slower to ignite and to retard flame propagation. Thermoplastic polymers can be rendered flame retardant by compounding with fire retardant additives, including halogenated organic compounds and inorganic compounds such as antimony oxide.
Brominated organic compounds have been used in both foamed and nonfoamed styrene polymer compositions, with most ignition-resistant styrene polymer foam products being made with a brominated fire retardant, optionally including a radical generator synergist or flow promoter. Of the various brominated organic compounds, typically only brominated aliphatics are utilized with vinylaromatic foams, with hexabromocyclododecane (HBCD) being the most common.
While effective in improving flame retardancy, the incorporation of flame retardant additives into thermoplastic polymer compositions can negatively impact the strength of the foam, particularly at higher levels of such additives. In non-foamed polymers, the bromine content is typically quite high, for example, in excess of 5 parts of bromine per 100 parts of styrene polymer. However, in foamed styrene polymers, the degree of bromine loading has to be significantly lower to avoid detrimentally impacting the structural qualities and skin quality of the foam.
For example, when utilizing HBCD as a fire retardant in a styrene polymer foam, a high level of HBCD is required in order to meet fire retardancy requirements, particularly the stringent European fire retardancy tests. Depending on the foam characteristics (for example, density, blowing agents, etc.), the amount of HBCD typically required to meet fire retardancy requirements is from 2.5 percent to 4 percent by weight of the styrene polymer (the higher the foam density, the higher the percentage of HBCD). However, the incorporation of HBCD into the styrene polymer foam at these levels may result in 1) a poor dispersion of the HBCD in the foam, resulting in non-uniform expansion and poor skin quality and 2) a high degree of degradation of the styrene polymer and of the regrinded material in the extrusion process due to excessive heating, resulting in reduction of the molecular weight of the styrene polymer foam and of the regrinded styrene polymer and a resultant drop in physical properties.
Therefore, there remains a need in the art for fire-retardant styrene polymer foams which utilize hexabromocyclododecane (HBCD) as the fire retardant, which meet fire retardancy requirements, and which are amenable to extrusion processes, but which do not exhibit poor structural qualities and/or skin qualities.
Those needs are met by the present invention. Thus, the present invention provides extruded, flame retardant, foamed styrene polymer compositions which utilize hexabromocyclododecane (HBCD) as the fire retardant, which meet fire retardancy requirements, and which are amenable to extrusion processes, but which do not exhibit poor structural qualities and/or skin qualities. The extruded, flame-retardant, foamed styrene polymer compositions of the present invention utilize a fire retardant formulation which is comprised of a mixture of hexabromocyclododecane (HBCD) and a phosphorous compound. The use of the phosphorous compound in the fire retardant formulation allows the use of less than about 2.5 percent of HBCD while maintaining a high level of fire resistance. Because a lower level of HBCD is utilized, the foams of the present invention do not suffer from poor structural qualities and/or skin qualities. Furthermore, the use of such a fire retardant composition allows a production of polystyrene foam with lower foam density, thus effecting appreciable cost savings.
Thus, in one embodiment of the present invention, there is provided a polymer foam composition comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than about 2.5 percent by weight, based on 100 percent of styrene polymer, of HBCD; and 2) from 0.1 percent to 4.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound.
In another embodiment, there is provided a polymer foam composition comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than about 2.5 percent by weight, based on 100 percent of styrene polymer, of HBCD; and 2) from 0.1 percent to 4.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound; and c) 0.01 percent to 0.2 percent by weight based on 100 percent of styrene polymer, of a flow promoter.
The present invention provides an extruded, fire-retardant, styrene polymer foam in which the fire retardant formulation is comprised of a mixture of HBCD and a phosphorous compound. The use of the phosphorous compound in the fire retardant formulation allows the use of less than about 2.5 percent of HBCD while maintaining a high level fire resistance. Because a lower level of HBCD is utilized, the HBCD is well dispersed in the foam and the foam is uniformly expanded with good skin quality. In addition, the presence of the phosphorous compound results in a lower density foam. A foam with lower density is formed even though the foaming temperature is lowered to account for the lowering of the glass transition temperature of the styrene polymer (due to the higher solubility of the phosphate compound in the styrene polymer).
The flame retardant foamed polymer compositions of the present invention comprise: a) a styrene polymer; b) a fire retardant formulation comprising HBCD and a phosphorous compound; and optionally, c) a flow promoter.
Suitable styrene polymers for use in the present invention include polystyrene or a copolymer formed from styrene monomer and copolymerizable ethylenically unsaturated co-monomers. The co-monomer content is typically less than about 50 percent, and preferably less than about 20 percent based upon the weight of the styrene polymer. Examples of copolymerized compounds include xcex1-methylstyrene, acrylonitrile, acrylic or methacrylic acids having one to eight carbon atoms, esters of acrylic or methacrylic acid with alcohols having one to eight carbon atoms, fumaric esters having one to eight carbon atoms, maleic anhydride or a small amount of divinyl benzene.
The HBCD portion of the fire retardant formulation is present in the styrene polymer foam in an amount less than about 2.5 percent by weight based on 100 percent of the styrene polymer, wit.h amounts less than 2.0 percent being preferred, amounts from 1.0 percent to 1.6 percent being more preferred, and an amount of 1.4 percent being especially preferred.
The phosphorous compound portion of the fire retardant formulation may be any organic compound which contains one or more phosphorous atoms and includes, but is not limited to, phosphates of the formula (RO)3PO wherein each R is independently selected from a substituted or unsubstituted, saturated or unsaturated, branched or straight-chain aliphatic moiety or a substituted or unsubstituted aromatic moiety. Suitable phosphates include, but are not limited to, triphenylphosphate (TPP), tributylphosphate, triethylphosphate, trimethylphosphate, tripropylphosphate, trioctylphosphate, diphenyl cresylphosphate, diphenyl methylphosphate, tris-(2-ethylhexyl)phosphate, isodecyl diphenylphosphate, isooctyl diphenylphosphate, bisphenyl diphenylphosphate, trixylil phosphate, and triisopropylphenylphosphate. Other phosphorous compounds suitable for use in the present invention are phosphites of the formula (RO)3P, phosphonates of the formula (RO)2RPO, phosphinates of the formula (RO)R2PO, phosphine oxides of the formula R3PO, phosphines of the formula R3P, and phosphonium salts of the formula R4PX, wherein each R is independently selected from substituted or unsubstituted, saturated or unsaturated, branched or straight-chain aliphatic moieties or substituted or unsubstituted aromatic moieties and X is a suitable counter ion, such as chloride or bromide. Of the above-described phosphorous compounds, phosphates are preferred and TPP is especially preferred.
The phosphorous compound is present in the styrene polymer foam in an amount from 0.1 percent to 4.0 percent by weight based on 100 percent of the styrene polymer, with 0.5 percent to 2.0 percent being preferred, with 1.0 percent to 2.0 percent being more preferred.
The polystyrene fire retardant formulations of the present invention may optionally include a flow promoter (melt flow modifiers) to assist initiation of the decomposition of the HBCD. By providing a source of reactive radicals (generated at a lower temperature than HBCD) which will abstract protons off the aliphatic portion(s) of HBCD and subsequently release the bromine radical, flow promoters are able to assist in the degradation of the HBCD. In addition, the reactive radicals from the flow promoter are capable of breaking down the styrene polymer chain during a fire, hence allowing the foam to melt away from the fire source. Suitable flow promoters include 2,3-dimethyl-2,3-diphenylbutane (that is, dicumyl or DMDPB); dicumyl peroxide, xcex1,xcex1xe2x80x2-bis-tert-butylperoxydiisopropylbenzene; bis(xcex1-phenylethyl)sulfone; 1,1xe2x80x2-diphenylbicyclohexyl; 2,2xe2x80x2-dimethyl-2,2xe2x80x2-azobutane; 2,2xe2x80x2-dichloro-2,2xe2x80x2-azobutane; 2,2xe2x80x2-dibromo-2,2xe2x80x2-azobutane; 2,2xe2x80x2-dimethyl-2,2xe2x80x2-azobutane-3,3xe2x80x2,4,4xe2x80x2-tetracarboxylic acid; 1,1xe2x80x2-diphenylbicyclopentyl; 2,5-bis(tribromomethyl)-1,3-4-thiadiazole; 2-(bromophenyl-5-tribromophenyl)-2,3,4-thiadiazole; dioctyl tin maleate; and dibutyl tin maleate. The most preferred flow promoter for use in the present invention is dimethyldiphenylbutane (that is, dicumyl or DMDPB).
Typically, when utilized, the flow promoter is present in the styrene polymer foam in an amount from 0.01 percent to 0.2 percent by weight based on 100 percent of the styrene polymer, with from 0.02 percent to 0.1 percent being preferred, and with 0.03 percent to 0.08 percent being especially preferred.
Various additives may also be incorporated in the present foam such as inorganic fillers; pigments, dyes, antioxidants, acid scavengers, ultraviolet absorbers, flame retardants, processing aids, dispersing agents, and extrusion aids.
Based upon the above, the following are typical flame retardant foamed polymer compositions of the present invention:
A polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than about 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.1 percent to 4.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than about 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.5 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 1.0 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than about 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) about 1.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.1 percent to 4.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of a flow promoter;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.5 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of a flow promoter;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 1.0 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of a flow promoter;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) 1.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of a flow promoter;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.1 percent to 4.0 percent by weight, based on 100 percent of styrene polymer, of TPP;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.5 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of TPP;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 1.0 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of TPP;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) about 1.0 percent by weight, based on 100 percent of styrene polymer, of TPP;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.1 percent to 4.0 percent by weight, based on 100 percent of styrene polymer, of TPP; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of a flow promoter;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.5 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of TPP; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of a flow promoter;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 1.0 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of TPP; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of a flow promoter;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) about 1.0 percent by weight, based on 100 percent of styrene polymer, of TPP; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of a flow promoter;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.1 percent to 4.0 percent by weight, based on 100 percent of styrene polymer, of TPP; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer of dimethyldiphenylbutane;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 0.5 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of TPP; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer of dimethyldiphenylbutane;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) from 1.0 percent to 2.0 percent by weight, based on 100 percent of styrene polymer, of TPP; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of dimethyldiphenylbutane;
a polymer foam, comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than 2.5 percent by weight, based on 100 percent of styrene polymer, preferably less than 2.0 percent, more preferably 1.0 to 1.6 percent, and most preferably 1.4 percent, of HBCD; and 2) about 1.0 percent by weight, based on 100 percent of styrene polymer, of TPP; and c) 0.01 percent to 0.2 percent by weight, based on 100 percent of styrene polymer, of dimethyldiphenylbutane.
The foams of the present invention may be prepared by extrusion processes well known to one of ordinary skill in the art.
A typical apparatus for making the foam according to an extrusion process is comprised of an extruder, a mixer, a cooler, and a die in series. Typically, the apparatus is maintained such that the feeding zone is maintained at 120xc2x0 C. to 160xc2x0 C.; the melting zone is maintained at 150xc2x0 C. to 190xc2x0 C., the metering zone is maintained at 180xc2x0 C. to 220xc2x0 C., and the mixing zone is maintained at 180xc2x0 C. to 200xc2x0 C. The fire retardant HBCD is in the form of a powder or as a granulate. Depending upon the physical state of the phosphorous compound (that is, liquid or solid), the phosphorous compound may be injected directly into the mixer, or introduced directly into the extruder. Alternatively, the phosphorous compound may be introduced in the form of a styrene polymer concentrate. The flow promoter, due to its required low concentration, is usually used in the form of a styrene polymer concentrate. All solid materials are fed to the extruder, while the liquid materials can be injected directly into the mixer. The fire retardant formulation and the other additives are mixed with the styrene polymer resin in the desired ratio. The blowing agent is then incorporated into the blended polymer melt at an elevated pressure in the mixer to form a foamable gel. The temperature of the foamable gel is reduced to a suitable foaming temperature (typically about 120xc2x0 C.) by reducing the temperature of the cooling zone. The foamable gel is then conveyed through the die into a region of reduced pressure to form the foam, adjusting the die opening as required and expanding the foam between substantially parallel forming plates. The foam structure is preferably closed-cell, and has a closed-cell content of at least 90 percent according to ASTM D-2856. The foam structure preferably has a density of 16 kg/m3 to 80 kg/m3 according to ASTM D-1622. The foam further has an average cell size of 0.05 to 2.4 mm.
Suitable blowing agents for use in the present invention may be CO2 or mixtures of blowing agents in any of the following proportions:
wherein HFC-134 is 1,1,2,2-tetrafluoroethane, HFC-134a is 1,1,1-2-tetrafluoroethane, and HFC-152a is 1,1-difluoroethane.
Preferred blowing agents are 100 percent CO2, mixtures of CO2, water, alcohol, dimethyl ether, and hydrocarbon, and mixtures of HFC-134a, HFC-134 and/or HFC-152a, alcohol, and hydrocarbon. The blowing agent is typically used at a concentration of between 0.05 to 0.20 mole/100 g polystyrene.